Continuous hypochlorite process for bleaching cotton textiles



July 8, 1952 s. M. ROGERS CONTINUOUS HYPOCHLORITE PROCESS FOR BLEACHING COTTON TEXTILES Filed Sept. 20, 1949 CA US TIC 5A TURA TOR WITH SQUEEZER WITH SGUEEZERS HOT WATER WASHERS ACID JBOX HYPOCHLORITE JBOX CAUSTIC J'BOX WATER WASHER ACID SOUR/N6 WITH SQ EE HOT WATER WASHERS WITH souzezms 5A TURA TOR SOUR/NC J BOX HYPocHLmg m SA TUR/ATOR WITH saws-525R HYPOCHLORITATVE so WATER J 80X WASHER WITH 37 SQUEEZER 42 CLOTH 9 WATER WASHER wmv sausszsn HYPOCHLOR/TE a S w W R WITH SGUEEZER HYPOCHLORITE SATURATOR WITH SQUEEZER HYPOCHLORITE SATURATOR WITH SQUEEZER 5% .R Q a TM vM. m T m m U Patented July 8, 1952 CONTINUOUS HYPOCHLORITE PROCESS FOR BLEACHING COTTON TEXTILES Stuart M. Rogers, Syracuse, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York Application September 20, 1949, Serial No. 116,714

4 Claims. (01. 8108) This invention relates to the treatment of cotton textiles and more particularly refers to a new and improved process for effecting continuous bleaching of cotton cloth employing hypochlorite as the bleaching agent.

Unbleached cotton cloth contains many impurities such as starch, waxes, oils and other noncellulose constituents which impede the action of bleaching agents on the cloth necessitating preliminary treatment in order to bleach the cloth successfully. Thus the bleaching process, as practiced commercially and as considered herein, embraces a series of treatments with various reagents under different conditions of operation coacting to produce cloth having the desired degree of whiteness with a minimum amount of degradation.

Heretofore, hypochlorite bleaching processes have been carried out in a batch manner, generally involving a sequence of individual steps known as singeing, desizing, kiering, souring, bleaching and neutralization. Although the inefliciency of batch bleaching has long been recognized and many attempts have been made to convert it to a continuous operation, no one, to my knowledge, ever succeeding in perfecting a commercial process for continuously bleaching cotton textiles employing hypochlorite as the bleaching agent. One of the chief difficulties in adapting the batch to continuous operation was the requirement for expensive, time-consuming kiering, normally consisting of boiling the cloth under about 15 pounds gauge pressure for approximately 8 hours while circulating a 1% to 2% caustic soda solution through the fabric. Obviously, an 8 hour kiering treatment does not lend itself to continuous operation. When the time of kiering was appreciably shortened, it was found that the cotton cloth'was not adequately prepared for the hypochlorite treatment, thu resulting in cloth of inferior whiteness. In operations employing a shortened kiering time, attempts were made to improve the whiteness of the cloth by using hypochlorite solutions of high concentration and high temperatures, but the product was unsatisfactory since excessive degradation of the cotton fibers had occurred.

, Continuous processes for bleaching cotton textiles have been developed employing hydrogen peroxide as the bleaching agent. The bleaching action with hydrogen peroxide is conducted at high temperatures, 100 C. or higher, which, as previously pointed out, would result in excessive degradation of the cloth if hypochlorite were substituted for peroxide. Although commercial- 1y successful, a major disadvantage of 'continuous peroxide processes resides in the high material costs of peroxide bleaching solutions as compared to hypochlorite solutions.

Accordingly, it is an object of my invention to provide an eflicient, economical process for continuously bleaching cotton cloth with hypochlorite to produce cloth of high whiteness without significant degradation.

Another object of my invention is to provide a continuous hypochlorite bleaching process wherein each of the treating steps is effected in a relatively short time, thereby permitting the operation to be carried out in continuous manner.

A further object of my invention is to carry out the bleaching step of my process in multiple stages utilizing dilute hypochlorite solutions under low temperature conditions, thereby obtaining cloth with an improved degree of whiteness without significant degradation.

Other objects and advantages of my invention will appear from the following description taken in connection with the accompanying flow diagram which illustrates my invention diagrammatically.

I have discovered that when cotton cloth is continuously passed through a series of treatments involving substantially complete desizing, caustic treatment in direct contact with steam, and multi-stage bleaching with dilute hypochlorite solutions at low temperatures for short periods of time, highly whitened cloth may be obtained in a continuous manner without material degradation of the cloth.

A preferred method for carrying out the present invention involves continuously passing unbleached cotton cloth through a series of operations comprising subjecting the cloth to the action of a desizing agent to effect substantially complete desizing thereof, saturating the desized cloth with dilute caustic soda solution, squeezing the cloth to obtain approximate a 1.0 cloth 1.0 liquor ratio, heating the dampened cloth by di rect contact with steam for about one hour in a J box, immersing the caustic treated cloth in a dilute sulfuric acid solution thereby effecting a souring action on the cloth, bleaching the cloth by passing through a plurality of bleaching stages until the desired degree of whiteness is obtained, each bleaching stage comprising saturating the cloth with a sodium hypochlorite solution containing l to 10 grams of available. chlorine per liter, preferably 2 to 5 grams of available chlorine per liter, and having a pH value of 8.0 to 12.0, preferably 9.0 to 11, squeezing the cloth impregnated with sodium hypochlorite solution to obtain approximately a 1.0 cloth 1.0 liquor ratio, subjecting the cloth to the action of the hypochlorite liquor at a temperature below 40 0., preferably 20 to 30 C., for to 30 minutes, preferably about minutes, thereby effecting bleaching of the cloth, and neutralizing the resultant bleached cloth with an aqueous solution of sulfur dioxide.

Referring to the accompanying drawing diagrammatically illustrating the process of my invention, unbleached cotton cloth is introduced in either rope or open width form into the process to first effect desizing of the cloth. If the cotton cloth to be bleached is medium or heavy weight, i. e. cloth having 5.0 to 3.0 and 3.0 to 1.5 yards to the pound, respectively, it is essential to remove the sizing in order to obtain cloth having a high degree of whiteness. I have found, however, with light weight cotton cloth having more than 5.0 yards to the pound, a desizing operation, while desirable, is not essential.

Any well known method for desizing cotton textiles, e. g. saturation with solutions of enzymes and dilute sulfuric acid, may be utilized in my process. Preliminary to the action of a desizing agent on the cloth, it is frequently desirable to wash the fabric with hot water to partially remove impurities therefrom, particularly foreign particles which adhere loosely to the goods. This may be! readily accomplished by continuously passing the cloth through vats l, 3 and 5 containing water maintained at about 50 C. and expressing excess moisture from the cloth by means of respective squeeze rolls 2, 4 and 6. Any suitable means for continuously washing cloth, as illustrated by conventional vats I, 3 and 5 and squeeze rolls 2, 4 and 5, may be employed in the practice of my invention. It is unnecessary to completely dry the cloth after each washi ordinarily squeezing the cloth until its liquor content is approximately 70% to 100% will suflice.

The washed cloth continues its passage into a bath of a 1% to 5% acid solution, preferably about a 3% solution of sulfuric acid, contained in vat I, and is pressed to a dampened condition, i. e. a 1.0 cloth 0.5 to 2.0 liquor ratio, preferably about a 1.0 cloth 1.0 liquor ratio, by squeeze rolls -8 before entrance into J box 9. Vat 1 and squeeze rolls 8 may be of a design similar to vats l, 3 and 5 and squeeze rolls 2, 4 and 6. Substantially complete desizing, that is, removal of at least 90% of the sizing, may be conveniently accomplished by passing the dampened cloth through an enclosed empty container maintained at room temperature for the length of time required by the acid solution to dissolve the sizing; ordinarily between /2 to 2 hours, although usually one hour is suflicient. A widely used piece of equipment in the textile bleaching industry for this purpose is the so-called J box or J chute consisting of a hollow elongated vessel in the form of a J, usually open at both ends. I prefer to employ J boxes constructed of stainless steel lined with vertical wooden slats about 1 inch square in cross-section and spaced about 1 inch apart to enable the cloth to slide more readily therethrough and keep it out of direct contact with the metal of the box.

Desized cloth leaving J box 9 is passed through vats II and I 3 containing water maintained at about 50 C. for the purpose of extracting a substantial portion of the acid present in the cloth. After each washing surplus moisture is removed by squeeze rolls l2 and I4. The construction and operation of water washers II and I3 and respective rolls I 2 and M are similar to hot water washers I, 3 and 5 and squeeze rolls 2, 4 and 6.

The cloth is next saturated with a 1% to 8%, preferably about 4%, solution of sodium hydroxide contained in vat l5 and then squeezed to a dampened condition, preferably about a 1.0 cloth 1.0 liquor ratio, by squeeze rolls l6 Dampened cloth passes into J box I! wherein it is retained in direct contact with steam introduced into the box for a length of time sufficient to effect substantial removal of natural impurities present in the cloth; ordinarily about one hour suffices, although the time may vary from about one-half hour to about two hours, depending upon the nature of the impurities. J box retention times of such duration do not interfere with the continuity of operation since the cloth in rope or open width form can be folded in the box in a manner conventional in the art, the number of folds determining the length of time the cloth remains in the box.

Although caustic treatment in a J box, as proposed herein, does not remove impurities present in the cloth as completely as kier boiling in batch processes, the former has the advantage of not degrading cotton fibers to the same extent as kiering and, hence, is a preferable operation providing the cloth can be bleached to a satisfactory degree of whiteness. In addition, caustic J boxing possesses economical advantages over the kier boiling operation, such as utilizing comparatively simple, inexpensive equipment in place of expensive kiers and appreciably shortening the time of processing.

Following the caustic treatment the cloth is washed in vats l8 and 2| containing Water maintained at about 50 C. to remove most of the caustic present in the cloth. After each washing the cloth is damp dried by squeeze rolls l9 and 22.

The next treatment to which the cloth is subjected is known as souring, the action of a very dilute solution of a mineral acid on the fabric. This acid treatment neutralizes any residual caustic remaining in the cloth and also dissolves such foreign matter as is not attacked during the caustic treatment. Although souring is desirable in preparing cloth for bleaching, it may be dispensed with in some instances, depending upon the nature of impurities and the degree of whiteness desired.

Referring again to the drawing, caustic treated cloth is immersed in a bath of dilute acid solution, preferably a 0.5% solution of sulfuric or hydrochloric acid, in vat 23 and then passed through J box 24 where it is retained at room temperature to allow completion of the souring action; usually about one-half hour is suflicient. Free acid remaining in the cloth leaving souring J box 24 is washed with water at about 30 to 50 C. in vat 25 and surplus moisture expressed by squeeze rolls 26.

After completion of the souring treatment the cotton cloth is now in condition for bleaching with hypochlorite. I have discovered that the fabric can be bleached to a high degree of whiteness with a minimum amount of degradation of the cotton fibers provided the bleaching is conducted under the following combination of conditions: (a) Saturation of the cloth with a dilute hypochlorite solution containing 1 to 10 grams of available chlorine per liter, preferably 2 to 5 grams of available chlorine per liter, and having a pH value of 8.0 to 12.0, preferably 9.0 to 11.0; (b) damp drying the cloth saturated with hypochlorite solution by squeezing it to a liquor cloth ratio of 0.5:1 to :1, preferably about a 1.0 cloth 1.0 liquor ratio, and retaining the dampened cloth in a suitable container at a temperature below 40 C., preferably 20 to C., for about 5 to 30 minutes, preferably about 10 minutes; and (c) multi-stage bleaching, i. e. repeating the hypochlorite bleaching treatment until the desired whiteness is obtained.

In the practice of my invention the bleaching operation may be carried out in conventional apparatus such as vats, squeeze rolls and J boxes as illustrated in the drawing. Cloth is continuously passed from squeeze rolls 26 into a bath of dilute sodium hypochlorite solution in vat 21, damp dried by squeeze rolls 28 and then subjected to the action of the hypochlorite solution for a short period of time in J box 29, thereby effecting partial bleaching of the cloth. A large portion of the hypochlorite having been consumed by its action on the cloth in J box 29, the bleaching operation is therefore repeated by immersing the cloth in vat 3| containing dilute sodium hypochlorite solution, damp drying by squeeze rolls 32, and retaining the cloth in hypochlorite J box 33 for an additional short period of time to effect further bleaching of the cloth. Bleaching may be concluded by passing the cloth from J box 33 through vat 34, squeeze rolls 35 and J box 36 under conditions of operation simiof my invention at low temperatures has a marked advantage in steam cost and simplicity of operation over the prior art continuous processes which require bleaching at elevated temperatures.

Oxidized impurities resulting from the bleaching operation are washed out by passing the cloth through water maintained at about 30 to 50 C. in vat 31 and surplus moisture removed by squeeze rolls 38. From squeeze rolls 38 the cloth passes through vat 39 containing an aqueous solution of sulfur dioxide, thereby neutralizing any residual chlorine present in the cloth, after which liquor is expressed from the cloth by squeeze rolls 40 and the cloth thoroughly washed in vat l2 and surplus moisture expressed by squeeze rolls 43.

Whiteness of the cloth, as referred to herein, is determined by a General Electric reflection meter, designed to measure reflectance of samples of the bleached materials to a blue light, the,

results obtained being expressed as percentage reflectance as compared with reflectance of magnesium carbonate. A whiteness of 86% or higher is considered good, although 83% is passable. A whiteness in excess of 83% has been found diflicult to attain without material degradation of the cotton fibers. The term fluidity is a measure of the viscosity of a solution of the bleached cellulosic material in cuprammonium solvent and is of importance because of its close correlation with the tensile strength of the solid fibers. The fluidity is expressed in reciprocal poises, so that the lower the fluidity number, the higher the viscosity of the cellulosic fibers and, therefore, the less the degradation of the fibers. The fluidity numbers are determined by testing a, 0.5% soluinvention carried out on commercial plant scale:

Example 1.Cotton cloth in width form having the following specification:

39 inches wide 72x48 threads per square inch 2.4 yards per pound was saturated with an enzyme solution, squeezed to a 1.0 cloth 1.0 liquor ratio, passed through 2.0 box at room temperature where it was retained for one-half hour and then washed with water and squeezed to damp dryness, thereby effecting substantially complete removal of the sizing in the cloth. The cloth continued its continuous passage through a 0.5% sulfuric acid solution, was squeezed to a 1.0 cloth 1.0 liquor ratio, retained in a J box for one-half hour at room temperature, washed with watr and squeezed to express excess moisture. The desized cloth was then saturated with a 4.0% solution of sodium hydroxide, squeezed to a 1.0 cloth 1.0 liquor ratio and then subjected to direct contact with steam for about one hour in a J box. After the caustic treatment the cloth was soured by immersion in a 0.5% sulfuric acid solution, followed by retention in a J box for about one-half hour at room temperature, washed with water and squeezed to a damp condition. Next the cloth was subjected tothree stages of bleaching with hypochlorite. Each stage involved immersing the cloth in a sodium hypochlorite solution containing 2.5 grams of available chlorine per liter and having a pH of 10.5 to 11.0, squeezing the saturated cloth to about a 1.0 cloth 1.0 liquor ratio, and passing the cloth at room temperature through a J box for 10 minutes. Following the bleaching operation the cloth was neutralized with an aqueous solution of sulfur dioxide and washed. The resulting product had a whiteness of 87.7% and a, fluidity of 4.8'recipoises.

Example 2.-Cotton cloth having the specifications recited in Example 1 was treated in the manner therein described except that the sodium hypochlorite solution employed in this test contained 2.0 grams of available chlorine per liter and had a pH of 9.5 to 10, and that a two-stage bleaching operation with a J box retention time of 30 minutes for each stage was employed. The bleached cloth had a whiteness of86.5 and a fluidity of 2.8 recipoises.

Example 3.--This test follows all the conditions of Example 2 with the exception that the hypochlorite solution employed contained 2.5 grams of available chlorine per liter and had a pH of 11.0. The bleach-ed cloth had a whiteness of 87.1 and a fluidity of 3.0 recipoises.

For comparative purposes cotton cloth having the same specification as that used in Examples l-3 was treated by standard batch hypochlorite and continuous peroxide processes. The fluidities of the bleached cloths thus obtained were comparable to those obtained by my process, but the whiteness of these cloths was substantially lower, approximately 83%. From the foregoing it will be evident that my improved multi-stage bleaching process produces superior whites as contrasted to those obtained by the present commercial batch hypochlorite and continuous peroxide methods. Furthermore, I found that the process of my invention resulted in the saving of processing cost of at least 15% over either the batch hypochlorite or the continuous peroxide method for bleaching cotton textiles.

Although certain preferred embodiments of the invention have been disclosed for purpose'of illustration, it will be evident that various changes and modifications may be made therein without departing from the scope and spirit of the invention.

I claim:

1. A method of treating unbleached cotton cloth which comprises continuously subjecting said cloth to the action of a desizing agent to effect substantially complete desizing thereof, continuously dampening the desized cloth with a dilute solution of caustic soda, continuously passing the cloth in dampened condition through an enclosed container in direct contact with steam for a period of /2 to 2 hours, continuously passing the caustic treated cloth through a plurality of successive bleaching stages until the desired degree of whiteness is obtained, each bleaching stage comprising dampening the cloth with a sodium hypochlorite solution containing 1 to 10 grams of available chlorine per liter and having a pH value of*8.0 to 12.0 and retaining the cloth in dampened condition for a period of 5 to 30 minutes at a temperature below 40 C., and neutralizing the resultant bleached cloth with an aqueous solution of sulfur dioxide.

2. A method of treating unbleached cotton cloth which comprises continuously subjecting said cloth to the action of a desizing agent to efiect substantially complete desizing thereof, continuously dampening the desized cloth with a dilute solution of caustic soda, continuously passing the cloth in dampened condition through an enclosed container in direct contact with steam for a period of to 2 hours, continuously passing the caustic treated cloth through a pmrality of successive bleaching stages until the desired degree of whiteness is obtained, each bleaching stage comprising dampening the cloth with a sodium hypochlorite solution containing 2 to 5 grams of available chlorine per liter and having a pH value of 9.0 to 11.0 and retaining the cloth in dampened condition for about minutes at a temperature of 20 to 30 0., and neutralizing the resultant bleached cloth with an aqueous solution of sulfur dioxide.

3. A method of treating unbleached cotton cloth which comprises continuously passin the cloth through a series of operation comprising dampening the cloth with a to 5% solution of' sulfuric acid, passing the dampened cloth through a J box maintained at about room temperature for a period of /2 to 2 hours, dampening the acid treated cloth with about a 1% to 8% solution of caustic soda, passing the dampened cloth through a J box in direct contact with steam for a period of to 2 hours, impregnating the caustic treated cloth with about a 0.5% solution of sulfuric acid, passing the" impregnated cloth through a J box maintained at about room temperature for a period of less than 1 hour, passing the cloth through a plurality of successive bleaching stages until the desired degree of whiteness is obtained, each bleaching stage com prising dampening with a sodium hypochlorite solution containing 2 to 5 grams of available chlorine per liter and having a pH value of 9.0 to 11.0 and passing the dampened cloth through a J box at a temperature of 20 to 30 C. for a period of 5 to 30 minutes, and neutralizing the resultant bleached cloth with an aqueous solution of sulfur dioxide.

4'. A method of treating unbleached cotton cloth which comprises continuously passing the cloth through a series of operations comprising washing said cloth with 'hot water, dampening the washed cloth with a 1% to 5% solution of H2804, passing the dampened cloth through a J box at about room temperature for a period of about one hour, dampening the acid treated cloth with about a 1% to 8% solution of caustic soda, passing the dampened cloth through a J box in direct contact with steam for a period of about one hour, impregnating the caustic treated cloth with about a 0.5% solution of H2804, passing the impregnated cloth through a J box at room temperature for a period of about one-half hour, passing the cloth through three successive bleaching stages, each bleaching stage comprising dampening the cloth With a sodium hypochlorite solution containing 2 to 5 grams of available chlorine per liter and having apH value of 9.0 to 11.0 and passing the dampened cloth through a J box at a temperature of 20 to 30 C. for a period of about 10 minutes, and neutralizing the resultant bleached cloth with an-aqueous solution of sulfur dioxide.

STUART M. ROGERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Matthews, Bleaching and Related Processes,

Chemical Catalog Company, New York, 1921, pages 330, 338. (Book in Division 43.) 

1. A METHOD OF TREATING UNBLEACHED COTTON CLOTH WHICH COMPRISES CONTINUOUSLY SUBJECTING SAID CLOTH TO THE ACTION OF A DESIZING AGENT TO EFFECT SUBSTANTIALLY COMPLETE DESIZING THEREOF, CONTINUOUSLY DAMPENING THE DESIZED CLOTH WITH A DILUTE SOLUTION OF CAUSTIC SODA, CONTINUOUSLY PASSING THE CLOTH IN DAMPENED CONDITION THROUGH AN ENCLOSED CONTAINER IN DIRECT CONTACT WITH STEAM FOR A PERIOD OF 1/2 TO 2 HOURS, CONTINUOUSLY PASSING THE CAUSTIC TREATED CLOTH THROUGH A PLURALITY OF SUCCESSIVE BLEACHING STAGES UNTIL THE DESIRED DEGREE OF WHITENESS IS OBTAINED, EACH BLEACHING 